Either will do nicely. The main difference is that chips burn faster than chunks. If you plan to add just a handful or two of chips for a light smoke over 20 minutes or so, then the burn rate is not a real issue. But if you want to smoke your food for an hour or more, it might be more convenient to use chunks. Depending on their size and the amount of air getting to the fire, they will burn that long, or even longer. If you soak chips in water for at least 30 minutes before adding them to the fire (no need to soak wood chunks), you will prolong their burn significantly and they will smolder more than flame. Just be sure to drain the wood of water first so you don’t extinguish the fire.